1. Field of the Invention
The present invention relates to a technology for binding tools that serve to open and close rings, which are formed of ring members so as to be able to open and close, by means of a switching lever for filing or binding documents or the like.
2. Description of the Related Art
There have hitherto been widely known lever arch type binding tools which have a plurality of ring members fixedly secured to an inner surface of a cover body of a binder or the like in such a manner that the ring members can be opened by an operation of a lever.
As such a lever arch type binding tool, there is one described, for example, in a first patent document (Japanese utility model application laid-open No. S57-24077). The binding tool described in this document is provided with a strip-like base portion formed of a metal plate, two rings that are each formed of a plurality of ring members mounted on the base portion, and a switching mechanism with an operation lever that serves to change each ring to toggle between a closed ring posture and an opened ring posture. Those ones among the ring members constituting the two rings which are arranged at one side are constructed so as to be rotatable relative to the base portion in such a manner that the rings can be opened and closed by an operation of depressing the operation lever.
In the binding tool as described in the first patent document, in which the ring members at one side are constructed to be rotatable with respect to the base portion, the degree of opening of each ring is small and a portion thereof to be opened is limited to one side, and the operation lever protrudes in the vicinity of the rings in their open state, so operation efficiency upon binding or unbinding (taking out) documents or the like is poor.
In addition, in such a lever arch type binding tool, the switching mechanism is large in size and is located in a central portion between the two rings, and the lever extending therefrom protrudes in the vicinity of the rings in their open state, so the switching mechanism with the lever not only hinders the operation of binding or taking out the documents, etc., but also makes it difficult to remove or insert a lot of documents at a time.
In view of the above, the applicant for the present invention has already proposed a lever operated type binding tool for documents or the like, as described in a second patent document (PCT/JP2004/4912), which is constructed such that when two rings mounted on a base portion are in their opened ring postures, a switching lever can pass through an opened portion of each ring. In this binding tool, even when the rings are in their opened postures, it is possible to make a free end of said switching lever pass toward the outside of the rings thereby to put it into a shunt state. Accordingly, by preventing the switching lever from coming to a location at which the switching lever becomes a hindrance in the operation of taking out and putting in documents or the like, too, it is possible to improve workability or operation efficiency upon replacement of documents or the like.
In the binding tool described in the second patent document, bearing portions for a cam member, which lie at a base end of the switching lever, are formed in a cover portion that rises from the base portion. The bearing portions are constructed such that a pair of upright segments in spaced-apart opposition to each other rise upward from the center of the cover portion with a shaft pin, which serves as the center of rotation of the cam member, being arranged between the opposite upright segments. Therefore, a slightly large occupation space is needed in the center of the cover portion, and hence there has accordingly been a constraint in reducing the diameter of the rings. For example, in case of the ring diameter of about 32 mm or more, the function of the binding tool can be exhibited to a satisfactory extent, but with the ring diameter of less than 33 mm, the protruded portions including both the upright segments, etc., may sometimes hinder the operation of taking out or putting in documents or papers depending upon the kinds or types thereof.
In addition, since the cover portion is curved after rising from the opposite sides of the base portion and then further bent to rise vertically in the center thereof, there has been a problem that it is necessary to form curved portions at two locations until the upright segments are reached, thus making it difficult to enhance processing or working accuracy. The reduction in the processing or working accuracy results in instability of the position of the cam member, so it becomes impossible to make the cam member operate with high precision, and the function of the switching mechanism including the cam member will accordingly be reduced.